Semiconductor-based sensors which use capacitive measuring principles are known. They are used in the field of chemo- and biosensors. Sensors which make use of the selectivity of enzymes, for example, are referred to as biosensors. Biosensors in silicon technology in which an enzyme is fixed on the surface of the sensor are already known (DE 44 36 001 C2).
In one group of sensors, a chemical reaction takes place at the sensor which is selective for an ion or molecule and in which a change in pH value occurs at the same time. Examples of applications include the determination of heavy metals and pesticides in waste water, penicillin determination, and DNA analysis.
These sensors have in common that they are structured as pH sensors which are equipped with an additional sensitive layer for the analyte to be determined, the underlying pH-sensitive layer continuing to be active. This sensor principle results in a plurality of measurements having to be carried out in succession to be able to indicate the concentration of an analyte since the sensor detects both the pH value of a sample solution and the additional change in pH value resulting from the reaction of the analyte present in the sample solution with the second, sensitive layer.